Integrity of Infrastructure Materials and Structures

FOREWARD

Corrosion-induced deterioration of both reinforced concrete and steel bridges exposed to chlorides is a pervasive problem that challenges the design of new structures and the maintenance of existing ones. Because of concerns regarding long-term serviceability of epoxy-coated reinforcing steel in bridge decks and substructures, enhanced attention has
focused on these materials in recent years. An important consideration in the case of existing steel bridges is the development of monitoring methods and technologies for characterizing
the deterioration rate. For exposed steel surfaces, determination of the as-constructed deterioration rates is critically important for maintenance schedules, especially for weathering steels. Furthermore, for new construction, specification of unpainted weathering versus
painted steel bridges has important cost-performance implications. In addition, steel performance monitoring can be facilitated by sensor technologies where accessibility is difficult
(e.g., suspension cables, box beams, and cable stays). This investigation was initiated for two purposes: (1) to evaluate stainless steel (SS) type 2304 (UNS S32304) as a corrosion-resistant reinforcement in concrete and (2) to develop sensor technology for characterizing corrosion rate on existing steel bridges in situ.

Jorge E. Pagán-Ortiz
Director, Office of Infrastructure
Research and Development

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TECHNICAL REPORT DOCUMENTATION PAGE

1. Report No.
FHWA-HRT-09-044

2. Government Accession No.

3. Recipient's Catalog No.
N/A

4. Title and Subtitle
Integrity of Infrastructure Materials and Structures

16. Abstract
Corrosion of bridges, both of steel and reinforced concrete construction, constitutes a major maintenance problem for the
United States. In the case of reinforced concrete bridges, recent attention has focused on corrosion-resistant reinforcements because of concerns that epoxy-coatings, which are presently employed for corrosion protection, may not provide the
75- to 100-year service life that is now required for major structures. A component of this research addressed two aspects of serviceability of 2304 stainless steel (SS) (UNS S32304) as reinforcement in concrete bridges. The first aspect addressed concerns regarding possible susceptibility to stress corrosion cracking in chloride-contaminated pore water, and the second aspect focused on determination of the critical chloride concentration, CT, to initiate active corrosion. The latter effort involved both accelerated aqueous tests and longer-term exposure of reinforced concrete slabs. No stress corrosion cracking was detected, and a value was defined which CT exceeds.

In the case of steel bridges, an accelerated corrosion test was developed for weathering steel with a range of exposure conditions that demonstrated sensitivity to chloride environments. The protective oxide layer (patina) of weathering steel was degraded above 0.5 wt percent chloride. Above 1 wt percent chloride, the protective oxide could have been severely degraded. Sensors were able to indicate the corrosion rate of coupon material exposed to the same environment. Sensors allowed direct and immediate observation of the impact environmental changes had on corrosion rate. X-ray diffraction showed that the corrosion products produced in cyclic test chambers were similar to those observed under field conditions. Sensors were capable of monitoring corrosive conditions within suspension bridge cables and other steel bridge geometries that were difficult to access.